Phosphate flotation



United States Patent 3,361,257 PHOSPHATE FLOTATION Joseph F. Haseman, Lakeland, Fla, assignor, by mesne assignments, to Armour Agricultural Chemical Company, a corporation of Delaware No Drawing. Filed Oct. 14, 1964, Ser. No. 403,932 3 Claims. (Cl. 209-166) This invention relates to phosphate flotation, and more particularly to the use of flotation modifiers in the flotation of phosphate ores with anionic reagents.

The recovery of phosphate values from phosphate ores has long presented a problem because of the complicated procedure required for such recovery. The process employed almost exclusively today is the so-called Crago process in which the deslimed and sized phosphate ore is subjected first to fatty acid and fuel oil flotation at controlled pH to produce a low-grade concentrate assaying 50 to 65 percent BPL. Sodium hydroxide is employed to provide the desired pH. The low-grade froth concentrate is then passed from the flotation cells to acid scrubbers Where it is scrubbed with sulfuric acid and washed to remove the fatty acid and oil. The washed concentrate is then floated with cationic reagents (amine) which separate most of the remaininig silica as a froth product which is allowed to go to Waste or to be recycled. The unfloated concentrate product from the flotation cells generally assays 73 to 76 percent BPL which is acceptable for phosphoric acid or fertilizer manufacturing.

The foregoing procedure is complicated since three separate processes are used to'obtain the final concentrate. Flotation reagent requirements are high. In addition, large quantities of water are required since it is necessary to thoroughly wash the feed before both the anionic (fatty acid) and cationic (amine) flotation steps. Further, procedures for the conditioning of feed with fatty acid reagents are critical, requiring close feed and in reagent requirements and costs, a substantial advance would be made in the field of phosphate flotation separation.

An object of the present invention is to accomplish the above result. A further object is to provide a process requiring only one flotation operation to produce a finished concentrate, with a reduction in reagent requirements and costs and an increase in phosphate recovery. A further object is to provide a process which tolerates relatively large amounts of -150 mesh slimes without seriously affecting reagent consumption or metallurgical results, so that the desliming and sizing of the feed is less critical. A further object is to provide a process permitting the plant to operate efiiciently at lower conditioning time and percent solids levels. Yet another object is to provide a process which greatly extends the pH range in which good conditioning and flotation are possible. Other specific objects and advantages will appear as the specification proceeds.

In one embodiment of my invention, I add to the anionic flotation feed, and preferably to the conditioning step of the separation, certain water-soluble chemical reagents as flotation modifiers along with the anionic reagent (fatty acid) and fuel oil. Such flotation modifiers include ammonia hydroxide and the amonium and sodium orthophosphates, pyrophosphates, metaphosphates, orthosilicates, metasilicates, fluorides, and carbonates. Other modifiers that have improved the separation are organic dispersing agents, such as the sodium and calcium lignin sulfonates.

For best results, I prefer to add the modifiers to the conditioning step of the separation. They may be added at the same stage of conditioning as the anionic reagent (fatty acid) and oils, but I prefer to add them ahead of thesereagents. In ordinary plant operation, several conditioning tanks, connected in series, are used to provide proper retention time. Thus, for example, it is preferable to add the modifier to the first conditioning tank and the anionic reagent and oils to the second tank. This permits the modifier to act on the mineral surfaces and properly prepare them for selective attachment of the flotation reagent when it is added at the later stage.

While many of the above-mentioned modifiers have been used in other separation operations for different metals and in different treating steps, I find that their use in the treatment of phosphate ores and in the fatty acid flotation step has the surprising result of reducing flotation reagent requirements while increasing the grade and recovery of phosphate in the concentrate in a single flotation operation Why the modifier functions to accomplish the above results, I am unable to state with certainty. It is possible that the modifier operates as a slime dispersing agent.

Without the addition of the modifier, the slime is in a flocculated condition and tends to coat the surfaces of both silica and phosphate grains. This coating retards or prevents attachment of the anionic flotation oils. I have found that slime tolerance is greatly increased by use of the modifiers.

It is also possible that the modifier may function as a precipitat ng or chelating agent for metallic or polyvalent cations. In anionic flotation, it is believed that attachment of the collector oil to the mineral surface is controlled by the presence of metallic or polyvalent cations, either in adsorbed form or as part of the mineral crystal lattice. These cations react with the collector to form an insoluble soap or oily film to which air bubbles: are attached to bring about froth flotation.

The phosphate ore suspension contains silica grains which have been activated by adsorption of polyvalent cations (mostly calcium) from the liquid phase. The suspension also contains phosphate grains, all of which have surface calcium ions as part of the crystal lattice. Normally, therefore, the activated silica grains would be floated along with the phosphate, thereby lowering the grade of the concentrate. Since the grade of the concentrate according to my process is not lowered, it is believed that the modifiers remove the adsorbed activating ions from the silica surfaces, thereby depressing silica flotation and increasing the grade of concentrate.

Among the flotation modifiers employed as above described, best results have been obtained through the use of sodium fluoride and the lignin sulfonates. Sodium fluoride and the lignin sulfonates have given outstanding metallurgical results. In the use of these modifiers as well as others heretofore listed, it is found that the addition of these to the conditioning step before the addition of the fatty acid-fuel oil mixture gives the best results in enabling the modifier to prepare the mineral surfaces for selective attachment of the flotation reagent. Thus, in an operation in which two conditioning tanks are employed in series, the modifier should be added to the first tank and the fatty acid mixture to the second tank.

As a specific illustration of the process, the anionic flotation feed in the conditioners (60 to 70 percent solids) is combined with the usual amounts of fatty acid and fuel oil as in regular anionic flotation procedure. Sodium hydroxide may be added to give the usual and desired pH. Although 68 to 75 percent solids is preferred, it is possible to obtain satisfactory conditioning with the proposed modifiers at a solids level as low as 60 percent. To the conditioners, I also add, preferably ahead of the point at which fatty acid and fuel oil are added, the flotation modifier in small amounts at rates of about 0.1 to about 2.5 pounds per ton of feed. The feed is then passed through the rougher flotation cells, with the rougher tails going to waste and the froth concentrate passing to the cleaner flotation cells. The cleaner tails may be passed to a low-grade concentrate bin at a grade of 60 to 70 BPL or they may be subjected to further processing. The cleaner concentrate provides a 60 to 90 percent BPL recovery and 73 to 76 percent BPL grade.

The foregoing process greatly improves the selectivity of the froth flotation separation of phosphate from silicious impurities with anionic-type collectors, eliminating two separation stages heretofore required in the recovery In laboratory flotation tests, the feed used in all instances was the same, essentially -35 +150 mesh in particle size, containing about 2 percent of -325 mesh slirnes, and assaying 29.0 percent BPL. The flotation procedure used for all tests was identical except for the addition of the modifier, caustic soda being used to adjust pH when necessary.

In the following tests, with the results set out in Tables I and II, fuel oil and fatty acid (2 parts fuel oil and 1 part synthetic tall oil) were used as a regular procedure,

air being added as usual. in the flotation step. In the tests,

certain modifiers are indicated by trade names, and these are identified as follows:

Norlig A is crude calcium lignosulfonate Marasperse N is refined sodium lignosulfonate Marasperse C is refined calcium lignosulfonate The process steps and results are set out in the following tables:

TABLE 1.EFFEOT OF MODIFIERS ON ROUGHER STAGE FLOTATION Modifier Product Assay,

Tall 011 Rate, percent BPL BPL Recovery Lbs/Ton Feed Cond., in 00110., Example N0. P Percent Rate, Name Lbs/Ton Cone. Tails eed 1 (standard)... 1.5 9.2 74.1 15.5 56.1 2 (standard). 2.0 9.6 68.3 3.6 91.0 3 2.0 1.25 8.0 70.4 2.1 95.4 1.5 1.25 9.1 72.2 2.7 94.2 1.5 1.25 7.6 74.5 5.1 88.6 1.5 1.50 9.4 73.4 4.1 90.8 2.0 0.65 8.0 73.8 3.5 92.6 NaF 2.0 1.00 7.8 73.6 1.8 96.1 N84P207-10H2O 0.2 1.50 9.0 72 .0 3 .9 91.3 N11 0 .5 1.00 0 .0 73 .0 6 .3 92 .5 Norlig A 1.0 0.75 8.4 75.4 5.1 88 .1 Marasperse N"--- 0.5 0.75 8.9 73.3 1 .7 96 .2 lfiarasperse (G3- 0.75 9 .4 73.2 2.9 93 .8

arasperse 03 0.75 8.9 73.0 2.0 06.6

TABLE 2.USE OF THE INVENTION TO PRODUCE HIGH AND LOW GRADE CONCENTRATES BY ROUGHER-CLEANER FLOTATION PROCEDURE Modifier High Grade Cone. Low Grade Cone.

Example No. Tall 011 Rate, Assay, Percent Rate, Lbs/Ton Feed BPL Assay, BPL Name Lbs/Ton Dist., Percent Dist.,

Feed BPL Acid Percent BPL Percent Insol.

While in the foregoing specification I have set forth specific procedures in considerable detail for the purpose of illustrating embodiments of the invention, it will be understood that such detail or details may be varied Widely by those skilled in the art Without departing from the spirit of my invention.

I claim:

1. In a process for the recovery of phosphate values from phosphate ores containing silica activated by adsorbed polyvalent cations, in which process air flotation in an aqueous system is effected with fatty acid and fuel oil, the steps of adding to the phosphate ore and silica feed With said fatty acid and fuel oil about 0.1-2.5 pounds of sodium fluoride per ton of feed at a pH of about 7.6- 9.6 to remove said adsorbed polyvalent cations on said silica, and introducing air for floating said phosphate from said silica.

2. The process of claim 1 in which said sodium fluoride is added to said fuel before said fatty acid and fuel oil are added.

3. The process of claim 1 in which said feed material is of about '--325 +150 mesh.

References Cited UNITED STATES PATENTS 8/1934 Crago -2 209--166 X l/l935 Hasselstrom 209-166 X 7/1946 Clemmer 209l66 9/1946 Clernmer 2091 66 7/1947 Clernmer 209-166 3/1958 La Baron 209166 7/1963 Baarson 209-466 2/1967 Greene 209-166 X FOREIGN PATENTS 6/1950 France.

12/ 1939 Great Britain. 6/ 1939 Switzerland.

FRANK W. LUTTER, Primary Examiner. HARRY B. THORNTON, Examiner.

20 R. HALPER, Assistant Examiner. 

1. IN A PROCESS FOR THE RECOVERY OF PHOSPHATE VALUES FROM PHOSPHATE ORES CONTAINING SILICA ACTIVATED BY ADSORBED POLYVALENT CATIONS, IN WHICH PROCESS AIR FLOTATION IN AN AQUEOUS SYSTEM IS EFFECTED WITH FATTY ACID AND FUEL OIL, THE STEPS OF ADDING TO THE PHOSPHATE ORE AND SILICA FEED WITH SAID FATTY ACID AND FUEL OIL ABOUT 0.6-2.5 POUNDS OF SODIUM FLUORIDE PER TON OF FEED AT A PH OF ABOUT 7.69.6 TO REMOVE SAID ADSORBED POLYVALENT CATIONS ON SAID SILICA, AND INTRODUCING AIR FOR FLOATING SAID PHOSPHATE FROM SAID SILICA. 